1. Field of the Invention
The present invention relates to a supporting structure of optical elements, an optical apparatus such as an exposure apparatus constructed by using the supporting structure, and a method for manufacturing a semiconductor device by using the optical apparatus, etc., and in particular relates to a supporting member for supporting an optical element such as a lens and a mirror, and an optical apparatus with a high degree of accuracy which comprises the supporting member for supporting the optical element, the optical apparatus being an exposure apparatus for use in manufacturing semiconductor integrated circuits, for example.
2. Description of the Related Art
A semiconductor exposure apparatus is an apparatus for transferring a negative plate (reticle) having a circuit pattern onto a substrate (silicon wafer). During the transferring, a projection lens is used for forming an image of the reticle pattern on the wafer, and high resolution of the projection lens is required for forming a highly integrated circuit. Accordingly, the lens for the semiconductor exposure apparatus is supported to have small aberration.
In view of such conditions, lenses for the semiconductor exposure apparatus demand uniformity in various characteristics of glass and films and high processing accuracy of a glass figure and assembling accuracy.
A lens barrel for holding glass used for lenses is generally made from a metal and materials different from glass are used therefor.
FIG. 11 illustrates part of an optical system of a conventional semiconductor exposure apparatus and shows a structural concept of the lens barrel. In the drawing, plural lenses 101 and 102 are fixed to metallic frames 103 and 104 for holding the lenses, which are further placed within a supporting member 105 and are urged and fixed thereto from upward movement by retaining screw-rings 107 and 108, respectively.
However, in the structure of the conventional lens barrel mentioned above, upon changing of ambient temperature, since the lenses and lens barrel elements respectively change in shape, the aberration thereof may change. In an exposure apparatus especially using a light source with a short wavelength, lenses are made from quartz or fluorite; since materials of the lenses and the lens barrel elements differ in the thermal expansion coefficient from each other, they cannot expand or shrink simply and freely without restriction from outside, respectively; consequently, the lens figure largely changes, thereby such deformation due to temperature changes largely affects the aberration of the lenses. Plural supporting members 105 are generally overlaid one on another to be arranged in the axial direction; when an external force is applied thereto during the connection thereof by overlaying or due to other reasons, the metallic frame for holding the lens is pressurized so that the lens is subjected to an external force from the screw-rings, etc., thereby deforming the lens figure, resulting in degraded performance of the optical system.
Also, in the conventional example mentioned above, the lens placed within the inner radius of the metallic frame becomes deformed due to gravity; by reasons that the direction and amount of such deformation depend on the figure of a lens placing portion an it is difficult to process the planar figure of the lens placing portion with a higher accuracy than that of the lens, and it cannot be assumed in advance that how the lens abutting the lens placing portion becomes deformed because each workpiece of the portion differs from one another, it is necessary that various kinds of aberration be corrected by predetermined adjustment of the lens posture or positions after checking the optical performance in the assembled optical system, which requires high accuracy in the deformation, resulting in an increased number of steps for assembly and adjustment.
In order to solve such problems, Japanese Patent Laid-Open No. 2000-66075 discloses that a lens is supported at plural points and the rotational angle of an optical element is adjusted so as to reduce the aberration of the entire optical system, which results from each optical element deformation produced by the lens support. However, in this structure, it is known that upon changes in ambient temperature, the lens surface is deformed due to the thermal expansion coefficient difference between the lens and the metallic frame (when the lens is supported with three-point supporting, the 3θ deformation sensitively changes relative to the temperature), so that the desired optical performance cannot be obtained.